1. Field of the Invention
The invention relates to high frequency transmission line electromagnetic signal mixers and more particularly to such signal mixer devices in which the entire mixer circuit is disposed as a planar integrated configuration mounted at right angles to the direction of input signal propagation.
2. Description of the Prior Art
In general, high frequency signal mixers, especially those designed to operate with carrier signals above 30 GHz, have been built in wave guide cavities in order to minimize losses and to permit incorporation in the structures of necessary filters. But when constructed integrally with other receiver components, the arrangement of the various interconnecting wave guides has presented formidable problems barring achievement of fully acceptable cost, package size, and system bandwidth, as well as of sufficiently low losses.
Stemming from the historical cross-bar structure for mixers, more recent balanced configurations have been realized in rectangular and ridged wave guide. Other hybrid integrated mixer designs have also been generated, using combinations of fin-line, co-planar, microstrip, and standard rectangular wave guide, and with the integrated mixer circuit disposed parallel to the direction of electromagnetic energy propagation.
In a letter to the editor in pages 450, 451 of the April 1974 issue of the I.E.E.E. Transactions on Microwave Theory and Techniques entitled: "Low-Noise Mixer in Oversized Microstrip for 5-mm Band", P. J. Meier disclosed a single ended signal mixer printed on a dielectric substrate disposed perpendicular to the signal propagation direction. It consists of a single-ended planar monopole detector circuit used also as a mixer by injecting the carrier signal as well as the local oscillator signal through a single rectangular wave guide across which the monopole and mixer diode are mounted.
The Meier mixer suffers from some of the problems present in the other prior art and undesirably requires a directional coupler to inject the local oscillator energy. The directional coupler increases the noise figure of the assembly because of losses inherent in the coupler. Because the local oscillator energy is injected at a considerable distance, electrically two or three wave lengths from the mixer diode, the total mixer assembly can not be truly characterized as a planar structure. Generally, the Meier device suffers from poorer isolation between the local oscillator and carrier frequency inputs. Also, suppression of local oscillator noise is inferior. In addition, the configuration is not amenable to the mounting of several mixers on one substrate or to the distribution of a local oscillator signal in a planar structure.